Many electronic circuits, such as integrated circuits, include various external components which are connected to the circuits during fabrication of a device. External components are often used, for example, to furnish selectivity of device performance. In other circumstances, an integrated circuit utilizes external components because integrated components cannot furnish suitable parametric values such as resistances and capacitances. Furthermore, some devices employ adjustable components which cannot be supplied in an integrated device.
A problem arises when an external component is not connected to the circuit. This problem can occur when an external component fails or when an external component is inadvertently omitted from connection to the device.
When an external component is missing, the circuit generally fails to operate in the intended manner. In some conditions, an external component may cause a circuit to fail. Occasionally, a dangerous condition arises when a component is missing.
What is needed is a circuit that detects the presence or absence of a component and generates a signal indicative of the absence of the component.